Trigger circuit with memory action



Oct. 13, 1959 K. G. KING ETA TRIGGER CIRCUIT WITH MEMORY ACTION Filed June 13. 1956 J M II Wm 5 L 7 U ..m% w k FEM 9 Z 0 :15 5 F 5.5 L I yard/2g (6126.

H all, 7 w. 5 N :1: 5 M 4 2w 1 0 a: a... ti 9 2 W @3 5 E C C- illilz m w mm w "MM (m emw m United States Patent TRIGGER CIRCUIT WITH MEMORY ACTION Kenneth Gordon King and Arnold William Tucker, London, England, assignors to Westinghouse Brake and Signal Company, Limited, London, England Application June 13, 1956, Serial No. 591,047 Claims priority, application Great Britain June 20, 1955 1 Claim. (Cl. 323-66) Our invention relates to a trigger circuit which employs a saturable reactor having two stable operating states. More particularly, 'our invention relates to a trigger circuit having inherent characteristics such that when the circuit is energized, following a period of deenergization, it will return to the stable operating state that it had prior to the period of deenergization.

Trigger circuits that have been used in the past and which employ saturable reactors have the disadvantage that their operation depends on a continuous energization of a control winding by a biasing source, with the result that a spurious output is provided if the source fails.

It is, therefore, an object of our present invention to provide a trigger circuit, employing a saturable reactor, that will overcome this difficulty.

Another object of our invention is to provide a trigger circuit, employing a saturable reactor that supplies its own biasing current to provide stable operation in either one of two stable operating states.

It is a further object of our invention to provide a trigger circuit, employing a saturable reactor, having two stable operating states and which may be switched from one operating state to the other by momentarily energizing a control winding.

Another object of our invention is to provide a trigger circuit, having two stable operating states, with memory action so that when it is energized, following a period of deenergization, it will return to the operating state that it had prior to the deenergization period.

In practicing our invention, we provide a saturable reactor with an alternating current winding, a feed-back winding and a control winding. The alternating current winding is connected, in series with a load circuit, to a source of alternating current energy. The feed-back winding is connected through a rectifying means in series with a choke coil to the load circuit.

The circuit parameters are chosen so that, when the saturable reactor is saturated and the apparatus is supplying a maximum load current or voltage, the magnetizing force provided by the feed-back winding is sufiicient to keep the reactor saturated so as to sustain that load voltage. On the other hand, when the saturable reactor is supplying a minimum load current or voltage, the magnetizing force provided by the feed-back winding is reduced to the extent that it provides no appreciable saturating effect in the reactor with the result that the minimum load volage is sustained. The reactor may be switched from supplying the maximum load voltage to supply the minimum load voltage by the application of a current of the appropriate polarity. This current may be either continuous or in the form of a pulse, to the control winding.

Other objects and features of our invention will become apparent from the following specification taken in connection with the accompanying drawings.

Referring now to the drawings,

Fig. 1 is a diagrammatic view showing one form of apparatus embodying our invention.

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Fig. 2 is a diagrammatic view showing a second form of apparatus embodying our invention in which the alternating current windings of the reactor may be provided with only a few turns.

Similar reference characters refer both views.

Referring now to Fig. 1, there is shown a saturable reactor designated by the reference character l. The reactor, as herein shown, is provided with two alternating current windings 2 and 3 connected in a series aiding relationship and wound about the outside legs of a threelegged magnetic core structure 4. These windings are further connected in series with a load circuit 5 to a source of alternating current energy 6. The load circuit may be of any suitable type, and in the interest of simplicity, 'it is here shown in block form.

The voltage developed across the load circuit is supplied through a choke coil 7 to a rectifier 8. The load voltage is thereby rectified and the rectified current is supplied, through a resistor 9, to a feed-back winding 10 located on a center leg of the reactor core.

In the normal operation of the apparatus, the load circuit may be provided with either a relatively large current or voltage, which we will herein refer to as the on state, or it may be supplied with a relatively small current or voltage, which we will herein refer to as the oil state. A control winding 11, located on the center leg of the core structure, provides means for switching from the off state to the on state and vice versa.

To provide an understanding of the operation of the circuit, let it be assumed that it is presently operating in the o state. 7 Under this condition the load current and voltage are relatively small and the feed-back winding is thereby provided with a relatively small current. Hence, the feed-back winding provides practically no magnetizing force. There is practically no saturating flux in the reactor core and the impedance of the alternating current windings is relatively high. This high impedance limits the flow of current through the load circuit to a relatively low value which is necessary to sustain the off state.

If the control winding is now energized with a current of the appropriate polarity, referred to herein as the normal polarity, from some triggering means, not shown, the center leg of the core structure will be provided with a unidirectional flux. This flux passes through the outside legs of the core structure and reduces the impedance of windings 2 and 3 so that additional current is permitted to flow from the source to the load circuit. This increases the load voltage which, in turn, is rectified and supplied to the feed-back winding in such a direction as to provide additional magnetizing flux. This further reduces the impedance of windings 2 and 3 and permits more current to flow to the load circuit to further increase the load voltage. The increased load voltage further increases the current in the feed-back winding to provide an additional increase in the flux of the reactor core. This action continues until equilibrium is reached; that is, the load circuit is provided with a voltage of sufficient magnitude so as to provide the core structure with a flux that will adjust the impedance of the alternating current windings to a value that will sustain the relatively large load voltage. The load voltage is sustained even though the energizing source for the control winding is removed, since the feed-back winding provides the reactor core with sufficient saturating flux to sustain the load voltage. This establishes the on state.

At any desired time the apparatus can be returned to the off state by applying a current of the opposite polarity, herein referred to as the reverse polarity, to the control winding. The magnetizing force produced by the control winding produces a flux which opposes the flux produced by the feed-back winding. This increases the to similar parts in impedance presented by the alternating current windings to the flow of current from the source 6 which, in turn, reduces the load voltage. The lowering of the load voltage results in a decrease in the flux produced by the feedback winding and further increases theirnpedance of the alternating current windings. This action continues until equilibrium is again'attained, which is the off state. In this condition the load current isres tricted by the impedanc'e of the load circuit and the impedance of the alternating current windings. The feed-back winding has relatively little effect.

"Hereinbefore we have considered the action of the apparatus insofar as the performance of triggering action is concerned. However, the apparatus possesses'a further feature in that, with certain proportioning of the circuit parameters, when the apparatus is energized following a period of deenergization, it assumes the operating state which it had prior to the period of deenerigization.

In cases where it is desirable to employ a saturable reactor with alternating current windings consisting of only a few turns, the'circuit arrangement shown in Fig. 2 may be advantageously employed. Referring now to Fig. 2, there is shown a trigger circuit somewhat similar to that discussed hereinbefore, but which employs transformers between the load circuit and the feed-back circuit for" impedance matching and isolation purposes. The current flowing through the alternating current windings of the saturable reactor is divided between the primary winding'lS of transformer 16 and a primary winding 18 of a transformer 19. These primary windings are here shown connected in a parallel relationship, but it is to be understood that they might, equally as well, be connected 'in a series relationship.

The load circuit is connected to a secondary winding 17 of transformer 16 while the rectifying means supplying the feed-back winding is connected through a choke coil 7 we secondary winding 20 of transformer 19.

'As here shown, transformers 16 and 19 are each provided with a greater number of secondary turns than primary turns. With this arrangement, the current flowing from the source 6 is restricted by the impedance of windings 2 and 3 of the reactor and by the impedance reflected into the primary winding circuits of transformers 16 and 19. Since these transformers have a relatively high turns ratio, that is, the ratio of the number of secondary turns to the number of primary turns, the impedance presented to the system by the transformers may 'be relatively low compared to the impedance "presented by the alternating current windings 2 and 3; thus; the flow of current from source 6 is controlled almost exclusively by the saturable reactor. 'With this arrangement two windings 20 and 21, embracing the outer legs of the reactor core, are connected in series with feed-back winding 10. The windings 20 and 21 are connected in a series opposing relationship insofar as the flux produced in the outside legs of the reactor core is concerned. Similarly, two windings 22 and 23 are placed on the outside legs of the reactor core and are connected in series with the control winding 11. The windings 22 and 23 are also connected in a series opposing relationship. The purpose of these additional windings is to cancel out the effect that faults, such as shorted turns and the like, may have upon the alternating current circuit.

The circuit shown in Fig. 2 like that of Fig. 1, also has the characteristic of a trigger circuit in that it may sustain either of two values of load voltage. The apparatus maybe switched from supplying one load voltage to the alternate load voltage by the application of a current of the appropriate polarity to the control winding 11. This circuit also possesses the additional feature of memory action, as does the circuit shown in Fig. l. 9

Although we have herein shown and described only two forms of apparatus embodying our invention, it is understood that various changes and modifications may be made therein within the scope of the appended claim without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

In combination with a source of alternating current energy, a trigger circuit comprising a three-legged magnetic core structure provided with a first, a second and a third pair of windings with one winding of each pair located 'on an outside leg of said core and a feed-back winding and a control winding located on the middle leg of said core, said first pair of windingsbeing connected in series aiding relationship; a first and a second transformer provided with a primary winding and a secondary winding, said primary windings being connected to said source of energy through said first pair of windings, a load circuit connected to said secondary winding of said first transformer, a choke coil, a rectifying means connected through said choke coil to the secondary winding of said second transformer, resistive means connecting said feed-back winding through said second pair of windings connected in a series opposing relationship to the output circuit of said rectifying means, and said third pair of windings connected in a series opposing relationship to said control winding whereby two operating states are established and switching action from one state to the alternate may be effected by the application of a current of appropriate polarity to said control winding.

References Cited in the file of this patent UNITED STATES PATENTS 

